1. Field of the Invention
The present invention relates to the fabrication of hollow elastomeric bodies having intricate shapes and, more particularly, to the fabrication of bladders for heart assist pumps.
2. Description of the Prior Art
A major problem in the provision of reliable prosthetics in contact with blood is the development of suitable materials for assist devices which must meet rigid requirements both mechanical and biological. They must have the requisite degree of elasticity, be rigidly non-toxic, and must be compatible with all components of blood. The materials must have an appropriate degree of elasticity for the specific end use application. They must retain this elasticity after many millions of flexing cycles in the body or other hostile biological environment and, therefore, must not be modified in that environment. They must not elicit foreign body response in the host, be rigidly non-toxic and must be compatible with blood neither causing thrombus nor clot formation destroying red cells.
Healing of the left ventricle of the heart of an animal, including man, is accelerated in certain situations if the ventricle can be relieved of some of its blood-pumping action by means of a suitable pump. One pump type requires a bladder affixed to rigid supports to serve as the active pumping element. Recently synthetic resin materials which are suitable, non-toxic substrates with full blood compatible surfaces have been developed. However, the methods for fabricating this material into a suitable bladder has not been satisfactory.
The main difficulty in fabricating these bladders is that they must be cast in a single piece since no seams, which would act as initiation sites for thrombus formation, can be tolerated. In addition, the bladder forms a virtually closed loop and can be removed from the male mold by peeling only if it is sufficiently flexible. Thermal forming by heat curing in a mold is not possible since the available materials are thermally degraded below the softening temperature. When it was attempted to spray a solution of the resin onto a mandrel, the material formed a mottled, rough product having uneven thickness and a tendency to form pinholes which is not permissible for the fabrication of an impervious bladder. The lost wax dip molding process was also unsuccessful since the bladder contains flanges with smooth, cylindrical, flat surfaces and sharp corners. This process can be utilized to separately fabricate the central body of the bladder and the flanges which are then secured by glue. This procedure introduces the possibility of later separation of the components which would result in failure and introduces a seam which serves as a site for thrombus formation and clotting.